In the standard specifications for so-called third generation radio telephony there are defined so-called Idle Periods (IPDL) in the downlink. These are used to support time-difference measurements (OTDOA) for location services e.g. sending information relevant to the currently determined locality of the radio device. In particular, the standards drafted by the 3rd Generation Partnership Project (3GPP) and numbered 3GPP Technical Specification (TS) 25.214 and TS 25.215 relate to this area.
Section 8 of 3GPP TS 25.214 v.4.0.0 (Release 99) relates to Idle Periods for IPDL location method. In general, during these idle periods all transmissions of physical channels from the base station with which the radio communications device or mobile station is in contact are temporarily ceased. In 3GPP, a base station is known as a Node B and a mobile station is known as UE (User Equipment).
IPDL (Idle Period in Downlink) location method is used, particularly in the FDD (Frequency Division Duplex) mode of WCDMA, to support time difference measurements between two cells by the UE. Idle periods are spaced at pseudo-random intervals in the downlink, whereby the entire transmission of a cell is turned off. A UE camped on such a cell can utilise these idle intervals for measurement of time-of-arrival of transmissions from distant neighbour cells, which would otherwise not be ‘visible’ to the UE due to the ‘near-far’ effect. Owing to the sudden decrease in overall received signal power seen by the UE during the first occurrence of an Idle period (caused by the serving cell switching its transmission off), the UE receiver gain needs to be increased. Otherwise clipping or added quantization noise to the received signal may occur, which could adversely affect baseband algorithms such as time of arrival measurement and Automatic Gain Control. The extent of the decrease in received signal power during an idle period can vary greatly, and will be dependent on a number of independent factors, e.g. proximity of the UE to the serving cell, the number of neighbouring cells, etc.